Ive spent the last year lifting heavier than I ever have, and Ive noticed quite a bit of stifness in my lower back from DL'ing. I would say Im extremely flexible(splits and pigeons are quite easy) that being said I think it becomes a disadvantage at some point to be too flexible. It helps out in injury prevention but alot of times I find myself in very awkward positions, especially in rubber guard. I would normally say try and be as flexible as possible, like any other aspect of fitness. But in this case I think it affects some of the positions and being able to pull off submissions